Just turn it on on, unless you have a leak, it's regulated, even cracking it open slightly has the same pressure as turning it fully open, it's just the flow your restricting and your not using enough for that to ne an issue.
No idea about the welding ones but the official advice for pub gas is to open the valve fully as it then seals on the outer stop and prevents any gas leaking out past the valve stem.
hotponyshoes, I believe that some of the USA bottles are fully opened for the same treason, prevents gas leaking from the spindle gland.
I only crack my BOC bottle open enough for current gas requirements,